The instant invention relates to laboratory testing devices, and more particularly to a whole body plethysmograph for use in making non-invasive pulmonary measurements of unrestrained small animals.
Whole body plethysmographs for non-invasive pulmonary measurements of small animals have heretofore been known in the art. For example, a biased-flow, whole body plethysmograph is described in an article "Aeroallergen-induced dyspnea in freely moving guinea pigs; quantitative measurement by bias-flow ventilated whole body plethysmography", by N. Chand et al, Allergy 1993: 48:230-235, Munksgaard 1993. The whole body plethysmograph illustrated on Page 231 of the article comprises a rectangular box having a bias flow inlet, a bias flow outlet, a transducer port, a reference bottle, and a water bottle. The reference bottle is connected to the rectangular box by a length of tubing and it is further vented to atmosphere by a length of tubing.
One particular shortcoming of the prior art plethysmographs is that the animal chambers have rectangular or other odd shapes. It has been found that these odd shapes do not promote uniform distribution of the aerosol injected into the interior of the box during testing. Still further, the aerosol injection devices of the prior art have not been found to be effective for evenly distributing the aerosol throughout the animal chamber. Accordingly, there are often uneven concentrations of aerosol which settle in the corners of the boxes. Another shortcoming of the prior art devices is that the reference chambers are separate from the animal chamber. It has been found that maintaining separate animal reference chambers introduces temperature, pressure, and ambient noise differences into the measurements which could affect the results of the testing.
The instant invention provides an improved plethysmograph comprising a cylindrical animal chamber and an integral reference chamber. The animal chamber and the reference chamber are provided in a cylindrical container wherein an internal bulkhead wall separates the two chambers. The reference chamber is situated above the animal chamber. The animal chamber and the reference chamber include ports for receiving differential pressure transducer leads. The animal chamber and the reference chambers also include ports for selectively venting each of the chambers. A port is provided in the bulkhead wall and a length of high resistance tubing is connected to the port for providing a high resistance bleed path between the animal chamber and the reference chamber. The plethysmograph further includes an aerosol manifold which extends into the top of the animal chamber. The aerosol manifold includes a plurality of radially extending apertures which open into the animal chamber for evenly distributing the aerosol in the animal chamber. The radial apertures essentially act as a showerhead for distributing the aerosol in the animal chamber. The plethysmograph still further includes two pneumotachographs in the top of the animal chamber for creating a pressure drop in the animal chamber during respirations. The plethysmograph may be used either in a volume mode of operation by plugging the pneumotachographs, or in a flow mode of operation by leaving the pneumotachographs unplugged. However, the preferred method of use is as a flow device. In the flow mode of operation, the air flows into the animal chamber through the pneumotachographs and outwardly through the multiple ports to a negative pressure reservoir via high-resistance tubing.
Accordingly, it is an object of the instant invention to provide a whole body plethysmograph for non-invasive pulmonary measurement of unrestrained small animals.
It is another object to provide a plethysmograph having a circular or cylindrical animal chamber.
It is still another object to provide a plethysmograph having a reference chamber integrally formed with the animal chamber.
It is a further object to provide a plethysmograph which can function either in a volume mode of operation or in a flow mode of operation.
It is yet object to provide an aerosol manifold having a plurality of apertures for evenly distributing aerosol in the animal chamber.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.